Batting first, England never really got the momentum after a top-order collapse despite skipper Eoin Morgan's brilliant counter-attacking 121 which took the team total to 234 in 47.5 overs. None of the other England players even crossed 30-run mark. Teams:
In reply, Warner's 115-ball 127 laid the foundation as Australia scored the required runs in 39.5 overs which ensured a precious bonus point for them, having achieved the target within 40 overs.
In the process, they lost a few wickets but they always had a firm grip on the proceedings.
Warner, who scored his third hundred in ODIs and the first in almost three years, started from where he left the Test series against India. He had scored three centuries in series, won 2-0 by his side.
Warner struck 18 boundaries and his most productive shot turned out to be the cover drive as he dispatched the England's quartet of Stuart Broad, Steven Finn, Chris Woakes and Chris Jordan in that region.
It was a fairly chanceless innings with exception of a sharp chance when wicketkeeper Jos Buttler failed to collect an edge off Jordan's bowling when he was on 70. He swept off-spinner Moeen Ali for a boundary to complete a well-deserved hundred off only 97 balls with 14 boundaries.
On reaching the milestone, Warner set his sights on a bonus point as he started to attack hitting four more boundaries. Warner hit Woakes for two boundaries before a back of the hand slower saw him miscue an inside out shot which ballooned up only for Ian Bell to catch at point.
Australia also lost Brad Haddin before James Faulkner scored the winning runs.
Earlier, it was skipper Morgan who came to England's resuce after a top-order collapse and single-handedly took his side to a respectable 234 as the visiting side slumped to 33 for four in the ninth over.
The top half of the England batting line-up were gone for 69 runs in the 16th over.
But Morgan, who took over England ODI captaincy recently from Alastair Cook, stood tall amid ruins as he anchored the visiting side's innings with a 136-ball 121 in the first match of the tri-series, also involving India.
Morgan struck 11 fours and three sixes in his superb knock after coming on to bat in the fourth over when his team score was at a precarious 12 for three.
Morgan shared a crucial 67-run partnership with wicketkeeper Jos Butler (28) for the sixth wicket to revive the innings. He stitched another 56-run partnership with Chris Jordan (17) for the eighth wicket before he was the ninth England batsman to depart in the 48th over.
None of the other England batsmen could make any substantial contribution with Butler (28) being the second highest scorer.
During the start of the match, Mitchell Starc extracted bounce from the SCG pitch and picked up two wickets in his first three deliveries.
He got opener Ian Bell from the first ball of the innings and then dismissed one-down James Taylor for a duck a delivery later as England lost two wickets without opening their account.
England then lost wickets at regular intervals with Starc claiming two more scalps later - that of Morgan and tailender Steven Finn (0) - while his pace colleague James Faulkner chipped in with three wickets for 47 runs. Pat Cummins, Glenn Maxwell and Xavier Doherty took a wicket each.
Starc got the right line and length in his first ball as Bell attempted to defend the ball that swung in and hit his right leg plumb in front of the stumps.
Taylor did not trouble the scorer as he tried to clip another inswinging delivery on the leg side but was beaten by the movement and struck in front of leg stump.
Promising England batsman Joe Root also did not last long as he fell to Cummins in the fourth over for five, edging a length ball straight to Shane Watson at first slip.
Opener Moeen Ali (22) showed some promise and looked like settling down along with Morgan to rescue the England innings.
Ali hit a huge six off Starc in the seventh over, clipping the ball off his pads to the wide long on boundary.
But he was out two overs later off the bowling of Faulkner with Glenn Maxwell taking an easy catch in the deep after the batsman drove the delivery on the up.
England: Eoin Morgan (capt), Moeen Ali, Ian Bell, James Taylor, Joe Root, Ravi Bopara, Jos Buttler, Chris Woakes, Chris Jordan, Stuart Broad, Steven Finn.
Australia: George Bailey (capt), Aaron Finch, David Warner, Shane Watson, Steve Smith, Glenn Maxwell, Brad Haddin, James Faulkner, Mitchell Starc, Pat Cummins, Xavier Doherty.
Batting first, England never really got the momentum after a top-order collapse despite skipper Eoin Morgan's brilliant counter-attacking 121 which took the team total to 234 in 47.5 overs. None of the other England players even crossed 30-run mark.